There is no known direct procedure available that allows a user to prescribe assembly loads for analyzing the integrity of a structure via computer implemented simulation. For example, in many situations fasteners that are used to assemble a structure must be affixed or fastened to the structure at a particular tension. If the fastener is affixed with too little tension it may provide too much vibration or movement in the structure causing the structure to be unstable, or may permit undesirable leakage through the gaskets. On the other hand, if the fastener is affixed too tightly, the fastener might break or cause damage to the structure. Thus, it is important that the fastener be affixed with the appropriate amount of tension.
One common example is the need for careful assembly of an automobile engine to run without leakage of gases or coolant. Automobile engines generally provide peak performance when the engine has "warmed up." In this situation, the engine becomes heated, along with the various elements or fasteners that are used in the engine. Therefore, the fasteners must be properly tensioned to hold the component correctly assembled without undue stress throughout the cycle of usage.
This process of properly tensioning the engine elements generally requires a significant amount of trial and error. This process is quite time consuming and can only be performed by technicians that are very familiar with engine tuning. Therefore, it is highly desirable to determine the optimal tensioning of the engine elements through computer simulation.
FIG. 1 is a simple example which illustrates the concept of an assembly load. In FIG. 1, cavity 2 is designed to be a sealed cavity. This is accomplished by placing the gasket 4 under pressure, which is done by initially pre-tensioning bolt 6 to a prescribed load value when connecting with flange 1. The pre-tension section 8 of the bolt 6, represented in FIG. 1, is then subjected to a tension load.
We have therefore realized that it is desirable to simulate the tightening of fasteners that are used to assemble a structure using a pre-tensioning capability.
We have also determined that it is desirable to apply a preload across the pre-tension section to simulate the tightening of a fastener for structural analysis and design.
We have further discovered that it is desirable to apply a tightening adjustment (displacement) of the pre-tension section, which also results in a preload of the fastener, to simulate the tightening of a fastener for structural analysis and design.
We have further realized that it is desirable to maintain the tightening adjustment so that the load across the fastener may increase or decrease upon loading of the entire structure during a sequence of loading steps that must be followed to perform structural analysis and design.